Timers: LTC timecode via the stage-display websocket

ProPresenter's HTTP API has no timecode route (verified: 21.4 returns
404), but its classic stage-display websocket still answers — so LTC now
comes from a stage layout field labeled "LTC": a zero-dependency RFC6455
client (stage-ws.js) authenticates (new stagePassword admin config),
resolves the LTC-labeled frame's uid from the layout list, and treats any
message carrying that uid as the timecode text. "Receiving" is a 2.5s
staleness heuristic; frozen or placeholder text reads as no-signal. The
HTTP probe stays authoritative when it ever answers (a 404 verdict is
retried once a minute), and the LTC card surfaces the reason when
timecode is unavailable (bad stage password, no LTC field). pp-timers-mock
grows a /stagedisplay websocket with --stage-pwd and --no-ltc-field to
exercise every path.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

modules/propresenter-timers/module.json

@@ -18,6 +18,11 @@
       "type": "password",
       "label": "API password (only if set in ProPresenter)",
       "default": ""
+    },
+    "stagePassword": {
+      "type": "password",
+      "label": "Stage display password (for LTC — ProPresenter Settings → Network)",
+      "default": ""
     }
   }
 }